Immediately
following a weight training exercise the muscle may seem full
and tight for 15 to 30 minutes, or 'pumped'. The muscular 'pump'
is caused by trapped plasma within the muscle. During muscular
contraction the contractile elements exert a force inward upon
themselves; the muscle diameter increases as it shortens. During
intense muscular contraction, this force inward momentarily occludes
the vasculature, backing up blood flow through that particular
muscle group. A compensatory increase of blood pressure forces
plasma from the congested capillaries into the interstitial spaces
of the muscle cells.
Bodybuilders commonly perform pumping-up
exercises before appearing on stage to make their muscles
appear fuller. For most of us there is no real benefit from achieving
a pump (except for boosting your ego). However, the inability
to achieve a pump is one symptom of overtraining
since fluid volume in the muscle, and possibly blood volume,
decrease when glycogen
stores are low. Intense cycling or swimming can also bring about
a pump, or temporary fullness in the working muscles.
The
burning sensation during certain weight training exercises or
high repetition training is caused by an accumulation of acid
in the fatiguing muscle. Anaerobic glycolysis utilizes carbohydrates
and produces water and acid, or free hydrogen ions. Lactate helps
prevent muscle acidosis by transporting positive hydrogen ions
out of the muscles. This acid does not clear sufficiently if
blood flow is impeded. The vasculature within the muscle is temporarily
occluded by the surrounding muscle when it is contracted intensely
for a relatively prolonged duration. The excessive acid acts
upon nerve receptors producing the localized burning sensation.
Excessive acid accumulation also impedes muscular contraction.
Acid interacts with calcium, rendering it unavailable for muscular
contraction. If repeated regularly, the muscle will begin to
adapt to this stress to become more efficient for later bouts.
See types
of muscular endurance and muscle
fatigue & blood supply graph.
Many basic or compound exercises (e.g.
squat,
bench
press, etc.) have a bell
shaped resistance curves or shift the resistance through
multiple muscle group throughout the exercise's range of motion
allowing the muscles to momentarily relax between repetitions.
This period of momentary relaxation between repetitions allows
greater opportunity for momentary blood flow permitting the clearing
of acid accumulation.
In contrast, auxiliary or isolated exercises (e.g., leg
extensions, lever
fly) tend to have relatively continuous resistance curves,
such as experienced on variable
resistance machines requiring the muscle to sustain contraction
through the majority of the exercise's range of motion. This
effect can be augmented by the use of cams
and variable
resistance levers which attempt to match the user's strength
curve by a preset resistance curve. In time, after adequate adaptation,
the muscle will be better able to deal with acid accumulation.
Also see types
of muscular strength.
Although the burning sensation may be indicative of the effectiveness
of the exercise as it pertains to a specific type
of muscular endurance, it does not efficiently promote strength,
power, or muscle development. In actuality, an exercise that
does not induce the burning sensation may be superior for the
development of strength and, possibly, muscular size. For example,
leg
press (basic and
compound) is noted
to be superior for both strength and muscular size to leg
extension (auxiliary
and isolated) where
the burning sensation is more prevalent. It is possible, however,
to supplement compound exercises (e.g. leg press) with isolated
exercises (e.g. leg extensions), in essence transferring muscular
endurance to muscular strength.
Judging the effectiveness of an exercise on the burning sensation
is fallacious. The burning sensation has nothing to do
with fat burning as popular believed (See spot
reduction myth).
It can also be misleading to judge an exercise's effectiveness
on a particular muscle group based upon local muscular
fatigue. For example, a common misconception is that leg raises
exercise the lower abdomen since most exercisers feel a burning
sensation in this area (see lower
abdomen myth). Furthermore, beginners often feel muscular
fatigue in unusual places until they become accustomed to that
exercise. This is similar to the 'weak link' analogy (i.e. A
chain is only as strong as its weakest link). Only after these
'weaker links' become conditioned will the 'chain' (target muscle
and assisting muscles) be exercised more effectively.
